Software could crash and markets suffer as a leap second is added to world time at midnight tonight

Airlines, trading floors and technology companies are braced for chaos today as world timekeepers prepare to add a leap second to global clocks.

Immediately before midnight dials will read 11:59:60 as clocks hold their breath for a second to allow the Earth’s rotation to catch up with atomic time.

When the last leap second was added in 2012 Mozilla, Reddit, Foursquare, Yelp, LinkedIn, and StumbleUpon all reported crashes and there were problems with the Linux operating system and programmes written in Java.

In Australia, more than 400 flights were grounded as the Qantas check-in system crashed.

Experts at Britain’s National Physical Laboratory (NPL) who will officially add the second to UK time, warned that markets which are already jittery from Greece could suffer transaction delays if their software was not prepared.

“There are consequences of tinkering with time,” said Peter Whibberley, Senior Research Scientist in the Time and Frequency group at NPL, who is known to colleagues as ‘The Time Lord.’

Every few years, we give one day an extra second. It's called a leap second. The International Earth Rotation and Reference Systems Service adds a leap second every few years to keep the clocks we use to measure official time and the speed of Earth's rotation in sync. But why do we need to do this? And what kind of problems could result?